Method of supplying lubrication oil in cold rolling

ABSTRACT

The present invention provides a method for supplying lubricant to various kinds of steel sheets with different qualities in cold rolling without any restrictions, such as lubricant supplying apparatus or lubrication conditions. This method comprises storing two or more kinds of lubricant such as A and B, having different compositions, selecting one lubricant or a mixture lubricant of the above A and B in accordance with the friction coefficient between the steel sheet to be cold rolled and a work-rolls, and supplying an emulsion comprising a mixture of the lubricant A and/or B and heated water.

TECHNICAL FIELD

The present invention relates to a method of supplying lubrication oilfor supplying lubrication oil to an inlet side of a rolling stand incold rolling of a metal sheet.

BACKGROUND ART

For example, in cold rolling of steel sheet, from the viewpoint of thestabilization of the rolling operation, shape and surface quality of theproduct, prevention of seizure, roll lifetime, etc., it is necessary tomaintain the friction coefficient between the rolled material (steelsheet) and work rolls at a suitable value. To obtain a suitable frictioncoefficient, a lubrication oil suitable for the grade and dimension ofthe rolled sheet and the rolling conditions is selected and is fed atthe inlet side of the rolling stand to the rolled steel sheet and therolls. In tandem cold rolling mill, in general, emulsion lubrication isused.

To obtain a suitable friction coefficient, increasing the emulsionsupplying rate or emulsion concentration is an effective means forimproving the lubricity and reducing the friction coefficient, but thisinvites an increase in cost. Further, there is a limit to the increasein the emulsion supplying rate or emulsion concentration in the currentstate due to limitations in facilities. As the limitation in facilities,for example, in the case of high concentration emulsion, sometimes thepipes become clogged or the capacity of an agitator in the tank impairsthe homogeneity of the high concentration emulsion. Further, the upperlimit of the emulsion supplying rate is determined by the pump capacity.

Recently, high tensile steel, TRIP steel, and other materials calledhard to produce materials are being rolled in an increasing trend. Withhard to produce materials, the rolling load becomes higher, so there isa need to reduce the friction coefficient and reduce the rolling load atthe front-end stands (e.g. 1st and/or 2nd stand) in the tandem coldrolling mill and to prevent seizure by reducing the friction coefficientand suppressing the friction heat in the rear-end stands which rollingrate becomes higher. That is, there is a need to reduce the frictioncoefficient in the entire rolling rate region compared with a mildcarbon steel when rolling a hard to produce steel sheet.

If schematically showing the case of use of a lubrication oil A wherethe friction coefficient becomes within the allowable range with respectto a mild steel, the result becomes as shown in FIG. 9. The lower limitof the allowable range of the friction coefficient is the limit at whichthe friction coefficient cannot be lowered further due to theperformance of the lubrication oil, restrictive conditions of thefacility, etc. explained above. Further, slip occurs even if there areno problems in restrictions of the facilities, so sometimes the frictioncoefficient cannot be lowered further. On the other hand, the upperlimit is determined by the seizure resistance in the boundary frictionregion of the lubrication oil. From experience with operations up tonow, the upper limit has been determined. The rolling conditions are setso that the friction coefficient becomes somewhat smaller than that. Upuntil now, mostly mild steel had been rolled, so lubrication oil A alonewas able to handle it. However, as clear from FIG. 9, to roll super hightensile steel with a tensile strength of for example 1270 MPa or more,lubrication oil A alone was not sufficient to obtain a suitable frictioncoefficient.

To solve this problem, the method of using a plurality of types oflubrication oil may be considered. For example, there is the method ofpreparing a low concentration and a high concentration lubrication oilby the same lubrication oil and supplying it to different supplyinglocations (for example, see Japanese Patent Publication (A) No.59-33023) or the method of selective use in accordance with the steelsheet thickness (for example, see Japanese Patent Publication (A) No.8-155510). However, as with these methods, even if using the samelubrication oil and changing the concentration, if considering thelimitations in facilities of the rolling mill or cost, it is difficultto handle the current plurality of rolled steel sheets.

Further, in another method of supplying lubrication oil, the method ofpreparing four tanks, prescribing three different types of lubricationoil, and selectively using them in accordance with the steel sheetthickness has been proposed (for example, see Japanese PatentPublication (A) No. 59-199109). This method uses four tanks and threetypes of lubrication oil and a detergent solution, but there is nodescription of the film thickness or the friction coefficient. Further,the method of classification of the grade and lubrication oil is alsorough. There are the problems that it is difficult to controllubrication sufficiently to meet all the strict requirements for surfacequality in recent years or all the small lots of various types of rolledsteel sheets and fine control is difficult.

Further, there is also the method of changing the mixing ratio of atleast two types of lubrication oil to change the composition of thelubrication oil in accordance with the quality characteristics requiredfrom the hot rolled steel strip for each hot rolled steel strip andsupplying the rolling oil comprised of the lubrication oil and water toat least one rolling stand (for example, see Japanese Patent Publication(A) No. 2000-351002). With this method, the lubrication oil supplyingrate is controlled in accordance with only the quality characteristicsrequired, so fine control was not possible.

DISCLOSURE OF INVENTION

The present invention has as its object to provide a method of supplyinglubrication oil able to handle a plurality of grades of metal (steel)sheets without being limited by the lubrication oil apparatus orlubrication control system in cold rolling of a metal (steel) sheet.

A method of supplying lubrication oil of a first aspect of inventionprovides a method of supplying lubrication oil for supplying an emulsionof a lubrication oil and heated water mixed together to an inlet side ofrolling stands of rolling mill in cold rolling of a steel sheet,comprising storing two or more types of lubrication oils of differentcompositions in separate tanks, selecting one of the stored lubricationoils in accordance with a friction coefficient between the rolled steelsheet and work rolls, and supplying an emulsion comprised of theselected lubrication oil and heated water mixed together to an inletside of the rolling mill.

A method of supplying lubrication oil of a second aspect of inventionprovides a method of supplying lubrication oil for supplying an emulsioncomprised of a lubrication oil and heated water mixed together to aninlet side of a rolling stand in cold rolling of a steel sheet,comprising storing the two or more types of lubrication oil of differentcompositions and at least one type of lubrication oil and at least onetype of additive in separate tanks, mixing two or more types oflubrication oil selected from the stored lubrication oils in accordancewith the friction coefficient between the rolled steel sheet and workrolls, mixing at least one selected lubrication oil and at least oneselected additive to obtain a mixed oil, and supplying an emulsioncomprised of this mixed oil mixed with heated water to an inlet side ofa rolling stand.

In the methods of supplying lubrication oil of the first aspect of theinvention and the second aspect of the invention, at least one of thelubrication oil may include an additive. Further, the method ofsupplying lubrication oil of the second aspect of the invention furthermay further comprise controlling an emulsion lubrication oil supplyingrate and/or emulsion concentration in accordance with the rolling rate.

A method of supplying lubrication oil of a third aspect of inventionprovides a method of supplying lubrication oil for supplying an emulsioncomprised of a lubrication oil and heated water mixed together to aninlet side of a rolling stand in cold rolling of a steel sheet,comprising storing two types of lubrication oils of differentcompositions and the lubrication oils and additives in separate tanks,setting in advance two mixing ratios of a first mixing ratio and secondmixing ratio in accordance with the friction coefficient for the twotypes of lubrication oil or a lubrication oil and additive, supplying afirst emulsion produced by the first mixing ratio to the inlet side ofthe rolling stand, increasing the emulsion supplying rate to reduce thefriction coefficient when the estimated friction coefficient duringrolling is larger than a target friction coefficient, switching to asecond emulsion produced by the second mixing ratio and supplying thesecond emulsion to the inlet side of the rolling stand when the increaseof the emulsion supplying rate reduces the friction coefficient, andswitching the second emulsion to the first emulsion to reduce theemulsion supplying rate and supplying the first emulsion to the inletside of the rolling stand when the estimated friction coefficient duringrolling is smaller than the target friction coefficient.

In the method of supplying lubrication oil of the third aspect of theinvention, at least one of the lubrication oils may include an additive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationship between the ranges ofapplication RA and RB of lubrication oils A and B of differentcompositions and two types of steel (mild steel and super high tensilesteel) in one embodiment of the first aspect of the invention.

FIG. 2 is a view schematically showing a rolling facility for workingthe method of the first aspect of the invention.

FIG. 3 is a graph showing the relationship between the range ofapplication RA of lubrication oil A and two types of steel (mild steeland low and medium grade high tensile steel).

FIG. 4 is a graph showing the relationship between the ranges ofapplication RA and RC of lubrication oils A and C of differentcompositions and two types of steel (mild steel and low and medium gradehigh tensile steel) in one embodiment of the second aspect of theinvention.

FIG. 5 is a view schematically showing a rolling facility for workingthe method of the second aspect of the invention.

FIG. 6 is a view schematically showing mixing of two types oflubrication oil and mixing of the mixed oil and heated water in therolling facility of FIG. 5.

FIG. 7 is a graph showing the relationship between the range ofapplication RA of the lubrication oil A and two types of steel (mildsteel and low and medium grade high tensile steel).

FIG. 8 is a graph showing the relationship between the ranges ofapplication RA and RD of lubrication oils A and D of differentcompositions and two types of steel (mild steel and low and medium gradehigh tensile steel) in one embodiment of the third aspect of theinvention.

FIG. 9 is a graph of the relationship between the range of applicationRA of one type of lubrication oil A and two types of steel (mild steeland super high tensile steel) in the conventional method of supplyinglubrication oil.

BEST MODE FOR WORKING THE INVENTION Embodiment of First Aspect ofInvention

In cold rolling steel sheet, mild steel and super-high tensile steel arerolled. Two types of lubrication oils of lubrication oil A andlubrication oil B of different compositions are used and are separatelystored in two tanks. As the lubrication oil, mineral oil, natural oil,synthetic ester, etc. may be used. Depending on the rolling conditions,these lubrication oils may also have an emulsifying agent, extremepressure agent, oiliness agent, or other additives added to them inamounts of 1 to 5 vol % or so with respect to the base oil. Further, thelubrication base oil does not have to be limited to two types. More thantwo types are good in that it increase the degree of freedom ofselection. However, if giving the explanation with respect to more thantwo types, the explanation would become complicated, so forsimplification, below the explanation will be given of two types oflubrication oil.

The lubrication oil A and lubrication oil B are fed as an emulsion to aninlet side of a rolling machine and used in the range of application ofthe lubrication oil. Here the “range of application of the lubricationoil” means a range in which the emulsion of the lubrication oil gives afriction coefficient allowable in terms of rolling operation and qualityof product. The range of application of the lubrication oil isdetermined by the type of the lubrication oil, emulsion supplying rate,and emulsion concentration.

As shown in FIG. 1, the range of application RA of the lubrication oil Aand the range of application RB of the lubrication oil B are mutuallyindependent and do not overlap in any portions. Mild steel is completelycovered by the range of application RA, while super high tensile steelis completely covered by the range of application. Therefore, the twolubrication oil tanks are switched in accordance with the frictioncoefficient between the rolled steel sheet and work rolls to select thelubrication oil to be supplied. The relationship between the rollingrate and friction coefficient and range of application of eachlubrication oil is found in advance by a test mill or operation recordsand are stored in a tabular format or by numerical equations in alubrication control apparatus comprised of for example a computer.

The selected lubrication oil and heated water are mixed and fed as anemulsion to the inlet side of the rolling machine. A suitable value ofthe mixing ratio of the lubrication oil and heated water is found inadvance by a test mill or operation records and set as a standardemulsion concentration in the lubrication control apparatus. Thetemperature of the heated water is 50 to 90° C. or so.

FIG. 2 shows an example of a cold rolling facility for working themethod of supplying lubrication oil of the first aspect of invention.The rolling facility is for example comprised of five stands. FIG. 2shows only the front-end stand of the rolling stand 10 and the laststand of the rolling stand 12. The rolling machines 10 and 12 arerolling stands which have four rolls, work rolls 14 and backup rolls 16.

The rolling facility is provided with lubrication oil tanks 20A and 20Bfor storing lubrication oils A and B, a heated water tank 40, and acooling water tank 50. The lubrication oil tanks 20A and 20B areconnected via lubrication oil pipes 21A and 21B to a main pipe 25, whilethe main pipe 25 is connected to a lubrication oil and heated watermixer 30 comprised of a static mixer. The lubrication oil pipes 21A and21B have lubrication oil pumps 22A and 22B, lubrication oil flow rateregulating valves 23A and 23B, and check valves 24A and 24B attached tothem. Further, the heated water tank 40 is connected through a heatedwater pipe 41 to which a heated water pump 42 and heated water flow rateregulating valve 43 are attached to the main pipe 25.

The front-end stands of rolling 10 and the rear-end stands of rollingstand 12 have emulsion headers 45 arranged at the inlet sides. Theemulsion headers 45 of the front-end stands of rolling stand 10 areprovided close to the steel sheet 1 and work rolls 14 and are providedwith a plurality of emulsion nozzles 47 along the sheet width direction.The emulsion headers 45 of the higher rolling rate rear-end stands ofrolling stand 12 are provided a distance to the upstream side from theroll bite considering the plateout time and are provided with aplurality of emulsion nozzles 47 along the sheet width direction. Thedistance between the emulsion nozzles 47 and roll bite is about 0.2 to 3m. The lubrication oil and heated water mixer 30 is connected to theemulsion headers 45 via the emulsion supplying pipes 31.

The rolling stands 10 and 12 are provided at their outlet sides withcooling water headers 55. Each cooling water header 55 is provided witha plurality of cooling nozzles 57 arranged along the sheet widthdirection. The cooling water tank 50 is connected to a cooling waterpipe 51 with a cooling water pump 52 and cooling water flow rateregulating valve 53 attached to it.

The rolling facility is provided with a lubrication control apparatus 60comprised of a computer. The lubrication control apparatus 60 is set inadvance with the emulsion supplying rate, the standard emulsionconcentration, etc. Based on these, it outputs operating signals to thelubrication oil flow rate regulating valves 23A and 23B, the heatedwater flow rate regulating valve 43, etc.

In a rolling facility configured in this way, when the steel sheet 1 ismild steel, the lubrication oil A is sent from the lubrication oil tank20A through the lubrication oil pipe 21A to the main pipe 25 by thelubrication oil pump 22A. Note that the lubrication oil flow rateregulating valve 23B of the lubrication oil B is closed and the flowrate becomes 0. On the other hand, heated water is sent from the heatedwater tank 40 through the heated water pipe 41 to the main pipe 25 bythe heated water pump 42. The heated water is heated in the heated watertank 40 and for example is held at 65° C. The lubrication oil A and theheated water are mixed at the main pipe 25 and flow into the lubricationoil and heated water mixer 30.

The mixed lubrication oil A and heated water are stirred in thelubrication oil and heated water mixer 30 to produce the emulsion EA ofthe lubrication oil A. The operating signal from the lubrication controlapparatus 60 is used to adjust the flow rates of the lubrication oilflow rate regulating valve 23A and the heated water flow rate regulatingvalve 43 and adjust to the standard emulsion concentration CA (mixingratio). The emulsion EA is supplied through the emulsion supplying pipes31 and emulsion headers 45 from the emulsion nozzles 47 to the inletsides of the rolling stands. Further, the work rolls 14 are cooled bycooling water sprayed from the cooling water nozzles 57.

In the case of super high tensile steel, the lubrication flow rateregulating valve 23A is closed and the lubrication oil B is suppliedfrom the lubrication oil tank 20B through the lubrication oil pipe 21Bto the main pipe 25. The emulsion of the lubrication oil B is producedand supplied to the inlet sides of the rolling stands in the same way asthe case of the lubrication oil A.

Embodiment of Second Aspect of Invention

In current day rolling, the ratio of super high tensile steel is aboutseveral %. Almost all of this is low and medium grade high tensile steeland mild steel with a tensile strength of up to 600 MPa. The range ofthe friction coefficient required in low and medium grade high tensilesteel is shown in FIG. 3. In low and medium grade high tensile steel,the increase in weight at the low speed part of the front-end stands incold tandem rolling mill is smaller than the case of mild steel, so itis sufficient that the friction coefficient of the extent of mild steelbe realized. However, if trying to realize high speed rolling, seizureis liable to occur, so it is necessary to reduce the frictioncoefficient to suppress the generation of heat by friction. In thiscase, with the lubrication oil A used up to now, the range of frictioncoefficient required in the speed range of the medium speed or morecannot be satisfied, so at the present, low speed rolling has to be usedand high speed rolling cannot be realized.

In this embodiment, two types of lubrication oils of differentcompositions may be mixed to realize low speed rolling and high speedrolling. For example, a lubrication oil C able to obtain a range offriction coefficient as shown in FIG. 4 is used. The lubrication oil Ccontains large amounts of an extreme pressure, oiliness agent, or otheradditive compared with a lubrication oil A and is generally expensive.For this reason, the greater the amount of use of the lubrication oil C,the higher the cost incurred. Therefore, the lubrication oil A and thelubrication oil C are mixed and the steel is rolled from the low speedto the high speed by a single mixing ratio by a range of the frictioncoefficient able to be taken by the lubrication oil A and lubricationoil C.

The inventors discovered that, except in special cases, even if mixingthe lubrication oil A and the lubrication oil C, without any chemicalreaction being caused, the friction coefficient at the time of mixingbecomes between the friction coefficients of the lubrication oil A andthe lubrication oil C. As the mixing method, two lubrication oil tanksstoring the lubrication oil A and lubrication oil C are prepared, theratio of supply from the lubrication oil tanks is changed in accordancewith the required ratio, and the oils are mixed in the middle of thepipe and agitated by the lubrication oil static mixer to produce a mixedoil. Next, the mixed oil and heated water are mixed and are agitated atthe mixed oil and heated water static mixer to obtain an emulsion whichis fed to the inlet side of the rolling mill.

In particular, when the range of application of the lubrication oil Aand the range of application of the lubrication oil C partially overlapas in FIG. 4, a single mixing ratio can be used to realize lubricationin most cases. Even if the ranges of application of the two areseparate, if the two are close enough, it is possible to set one type ofmixing ratio. The mixing ratios which can realize the ranges ofapplication and low speed to high speed rolling are found in advance bya test mill. Setting a single type of mixing ratio in advance accordingto the steel is simple in control. Since the type of steel sheet isstored in the lubrication control apparatus, without having to depend onthe operator, it is possible to roll the steel sheet while setting themixing ratio in accordance with the friction coefficient between therolled steel sheet and work rolls.

When making the emulsion supplying rate and emulsion concentration thesame as the time of use of the lubrication oil A, sometimes, by justmaking the mixing ratio of the lubrication oil A and lubrication oil Cconstant, sometimes it is not possible to realize a sufficiently smallfriction coefficient at the time of for example high speed rolling. Atthe time of ordinary rolling using the lubrication oil A, in many casesboth the emulsion supplying rate and emulsion concentration are set tobelow the maximum values, so it is possible to change the emulsionsupplying rate and emulsion concentration from the values at the time ofuse of the lubrication oil A. Therefore, it is possible to change theemulsion supplying rate or emulsion concentration in accordance with therolling rate so as to realize high speed rolling. In general, the factoreasy to change in accordance with the rolling rate is the emulsionsupplying rate. Therefore, first, the emulsion supplying rate ischanged. When the required friction coefficient cannot be obtained evenso, adopting the method of changing the emulsion concentration isdesirable.

To control the emulsion supplying rate or emulsion concentration, thefriction coefficient is measured on line and the measured frictioncoefficient is made to match the target value by changing the emulsionsupplying rate or emulsion concentration or by finding the relationshipbetween the rolling rate and the friction coefficient in advance andcontrolling the emulsion supplying rate or emulsion concentration inaccordance with the rolling rate. Note that when measuring the frictioncoefficient, there is the possibility of roll wear having an effect.Roll wear is highly correlated to the rolling tonnage, so therelationship between the rolling tonnage and the amount of wear is foundin advance and the roll wear is corrected for in control of lubricationaccording to the rolling rate.

FIG. 5 shows an example of a cold rolling facility for working themethod of supplying lubrication oil of the second aspect of theinvention. In FIG. 5, apparatuses and members similar to the rollingmills shown in FIG. 2 are assigned the same reference numerals anddetailed explanations are omitted. When the rolled steel sheet is mildsteel, the emulsion of the lubrication oil A is supplied to the inletsides of the rolling mills in the same way as the first aspect of theinvention.

In FIG. 5, lubrication oil pipes 21A and 21C from lubrication oil tanks20A and 20C are connected to a lubrication oil mixing pipe 27. Thelubrication oil mixing pipe 27 is connected to a lubrication oil mixer33, while the lubrication oil mixer 33 is connected through a main pipe34 to which a check valve 35 is attached to a lubrication oil and heatedwater mixer 36. The main pipe 34 between the check valve 35 and thelubrication oil and heated water mixer 36 has a heated water pipe 41connected to it. The lubrication oil and heated water mixer 36 isconnected through emulsion supplying pipes 37 to emulsion headers 45.

In the rolling facility configured in this way, when the rolled steelsheet is high tensile steel, in the low speed region where the frictioncoefficient falls in the range of application RA of the lubrication oilA, lubrication oil A is supplied from the lubrication oil tank 20Athrough the lubrication oil pipe 21A and mixing pipe 27 to the main pipe34. In the main pipe 27, the lubrication oil A and the heated water fromthe heated water tank 40 are mixed. Next, the mixed lubrication oil Aand heated water are agitated by the lubrication oil and heated watermixer 36 to produce an emulsion EA of the lubrication oil A. Thelubrication oil flow rate regulating valve 23A and the heated water flowrate regulating valve 43 are adjusted in their flow rates to adjust themixing ratio of the lubrication oil A and heated water. The emulsion EAof the lubrication oil A is fed through the emulsion supplying pipes 37and emulsion headers 45 from the emulsion nozzles 47 to the inlet sidesof the rolling stands 10 and 12.

In FIG. 4, in the intermediate speed region where the frictioncoefficient does not fall in the ranges of application RA and RC of thelubrication oil A and lubrication oil C, a mixed oil of the lubricationoil A and lubrication oil C is used. The lubrication oil A is suppliedfrom the lubrication oil tank 20A through the lubrication oil pipe 21Ato the mixing pipe 27, of the lubrication oil C is supplied from thelubrication oil tank 20C through the lubrication oil pipe 21C to themixing pipe 27. As shown in FIG. 6, the lubrication oil A andlubrication oil C are mixed in the mixing pipe 27 and the mixed oil MACis sent to the main pipe 34. On the other hand, heated water is fed fromthe heated water tank 40 through the heated water pipe 41 to the mainpipe 34 and is mixed with the mixed oil MAC. The mixed oil MAC andheated water are agitated by the lubrication oil and heated water mixer36 to produce an emulsion EAC of the mixed oil MAC of the lubricationoil A and lubrication oil C. The lubrication oil flow rate regulatingvalves 23A and 23C and the heated water flow rate regulating valve 43are adjusted in their flow rates to adjust the mixing ratio of thelubrication oil A and lubrication oil C. The emulsion EAC of the mixedoil. MAC is supplied through the emulsion supplying pipes 37 andemulsion headers 45 from the emulsion nozzles 47 to the inlet sides ofthe rolling stands 10 and 12.

In the high speed region, the friction coefficient completely falls inthe range of application RC of the lubrication oil C, so the sameprocedure is followed as with the low speed region lubrication oil A toproduce an emulsion MAC of the lubrication oil C and to supply it to theinlets of the rolling stands 10 and 12.

In this embodiment, the two lubrication oil tanks both store lubricationoil, but the invention is not limited to this. It is also possible tohave one tank store lubrication oil, have the other tank store theadditive, mix the lubrication oil and additive, and supply an emulsionof the mixed oil. There may also be three or more tanks. For example,when there are four tanks, it is possible to have three tanks storethree types of lubrication oil of different compositions and have theremaining tank store the additive or have two tanks store two types oflubrication oil of different compositions and have the other two tanksstore two types of additive of different compositions. In this case,three types of lubrication oil may be mixed, three types of lubricationoil and one type of additive may be mixed, two types of lubrication oiland two types of additives may be mixed, or other combinations may bemixed.

Embodiment of Third Aspect of Invention

Depending on the type of the lubrication oil, as shown by thelubrication oil D shown in FIG. 7, sometimes the range of application RDis far from the range of application RA of the lubrication oil A. Inthis case, depending on the steel, sometimes a single mixing ratio aloneis not enough to realize rolling from the low speed to the high speed.

In this embodiment, for mild steel, the lubrication oil A is used in theentire rolling rate region. For low and medium grade high tensile steel,as shown in FIG. 8, two mixing ratios of the first mixing ratio andsecond mixing ratio are set in advance. The second mixing ratio shouldbe set to any ratio in accordance with the rolled steel sheet etc.Further, one mixing ratio is selected from the two mixing ratios inaccordance with the friction coefficient, and the emulsion EAD of themixed oil MAD of the lubrication oils A and D mixed at the selectedmixing ratio D is supplied to the inlet side of the rolling mill by theemulsion supplying rate used in the emulsion EA of the lubrication oilA.

Further, since the amount of oil introduced to the roll bite does notincrease even if increasing the emulsion supplying rate, sometimes thefriction coefficient will not fall below a certain value. FIG. 8 setstwo ranges of application RAD1 and RAD2 considering this case. When thefriction coefficient will not decrease even if increasing the emulsionsupplying rate, the emulsion concentration is raised.

Further, when the friction coefficient will not decrease even if theemulsion concentration is increased, a second mixing ratio increasingthe good lubricity lubrication oil D is used. When increasing therolling rate from a low speed to high speed rolling, the frictioncoefficient is measured on-line. If the friction coefficient does notchange even with an increase of the emulsion supplying rate, a secondmixing ratio preset for high speed rolling is changed to. When switchingthe coil or otherwise returning to low speed rolling, with the secondmixing ratio, the friction coefficient becomes too small and there isthe risk of slip. In this case, the mixing ratio is returned to theoriginal first mixing ratio. The mixing ratios prepared in advance neednot be two types. In that case, if for example increasing the ratio ofthe good lubricity lubrication oil D in the order of the second mixingratio and third mixing ratio, if the friction coefficient is large evenwith the second mixing ratio, the third mixing ratio is changed to. Ifthe friction coefficient is large even with the third mixing ratio, thefourth mixing ratio is changed to.

The lubrication oil D may also be comprised of the lubrication oil Aplus an additive. Additives are currently often used for controlling thefriction coefficient at the time of high speed rolling. Additives aregenerally expensive, so in this invention, additives are not used in lowspeed rolling and are used in only high speed rolling. Due to this, itis possible to keep down the amount of use of the additives and reducethe rolling costs.

Note that the lubrication supplying method of the third aspect of theinvention can be worked by a rolling facility as it is shown in FIG. 5used for working the second aspect of the invention.

This invention is not limited to the above embodiment. The rolled steelsheet may be, in addition to steel, titanium, aluminum, magnesium,copper, or other metal and alloys of these metals.

The lubrication oil stored in a tank may have additives added to it inadvance. As the additives, an emulsifier, extreme pressure agent,oiliness agent, or another additive may be used. When mixing two typesof lubrication oil in the second aspect of the invention or the thirdaspect of the invention, both may be lubrication oil containingadditives, both may be lubrication oil not containing additives, or justone may be a lubrication oil containing additives. Further, when mixinga lubrication oil and additives, the additives mixed with the additivesmixed into the lubrication oil in advance may be same or different.

EXAMPLES

A single-stand 4Hi test mill was used to roll two coils joined tosimulate ordinary cold rolling. The rolled steel sheet, lubrication oil,emulsion supplying rate, and rolling rate range were as follows.

Rolled steel sheet: Mild steel and 590 MPa high tensile steel

Lubrication Oil:

-   -   Lubrication oil A (lubrication oil containing palm oil in an        amount of 35% and synthetic ester in 65% and having a viscosity        at 40° C. of 39 cSt)    -   Lubrication oil B (lubrication oil comprised of synthetic ester        in an amount of 100% and having a viscosity at 40° C. of 80 cSt)

Emulsion supplying rate: 5 liter/min

Rolling rate range: 200 to 1500 mpm

(1) An emulsion of the lubrication oil A at a concentration of 5% wasused to roll mild steel. As a result, rolling was possible with noproblem of seizure flaws from the accelerated/decelerated region of 200mpm to the highest speed 1500 mpm.(2) An emulsion of the lubrication oil B at a concentration of 5% wasused to roll mild steel. As a result, the friction coefficient was toosmall and slip occurred.(3) An emulsion of the lubrication oil B at a concentration of 3% wasused to roll mild steel. As a result, neither slip nor seizure occurred.(4) An emulsion of the lubrication oil B at a concentration of 2.5% wasused to roll mild steel. As a result, seizure flaws occurred duringrolling at 1500 mpm. A look at the purchasing prices of lubrication oilA and lubrication oil B shows that the price of the lubrication oil B is2.2 times that of the lubrication oil A, so from the results of (1) andthe results of (3), it could be confirmed that with mild steel, use ofthe lubrication oil A is economical.(5) An emulsion of the lubrication oil A at a concentration of 3% wasused to roll 590 MPa high tensile steel. No seizure flaws occurred at500 mpm.(6) An emulsion of the lubrication oil B at a concentration of 3% wasused to roll 590 MPa high tensile steel. As a result, no seizure flawsoccurred from 200 mpm to 1500 mpm.(7) Cost-wise, using the lubrication oil B over the entire speed regionis not wise. If using the lubrication oil. B over the entire speedregion, there is also the danger of slip, so the inventors studiedmixing the lubrication A with the lubrication oil B. The lubrication oilA and the lubrication oil B were mixed in amounts of 50% each to producea mixed oil. An emulsion of this mixed oil in a concentration of 3% wasused to roll 590 MPa high tensile steel. As a result, no seizure flawsor slip occurred from 200 mpm to 1800 mpm.

INDUSTRIAL APPLICABILITY

The method of supplying lubrication oil of the first aspect of inventioncomprises selecting one of two or more types of lubrication oil inaccordance with the friction coefficient between a rolled steel sheetand work rolls and supplying an emulsion of the selected lubrication oilto the inlet side of a rolling stands. Therefore, it has the effectsthat the lubrication oil supplying apparatus becomes simple and controlof lubrication becomes easy.

The method of supplying lubrication oil of the second aspect of theinvention comprises mixing two or more types of lubrication oilsselected from stored lubrication oils in accordance with a frictioncoefficient between a rolled steel sheet and work rolls or mixing atleast one selected lubrication oil and at least one selected additive toobtain a mixed oil and supplying an emulsion of this mixed oil to theinlet side of the rolling mills. At this time, by preparing two or moretypes of mixed oils able to realize the required close frictioncoefficient, it is possible to obtain a mixed oil able to realize afriction coefficient closer to that required. Therefore, finelubrication control becomes possible.

A method of supplying lubrication oil of a third aspect of the inventioncomprises setting in advance two mixing ratios of a first mixing ratioand second mixing ratio of two types of lubrication oil or a lubricationoil and additive in accordance with the friction coefficient, selectingone of the two mixing ratios in accordance with the estimated frictioncoefficient during rolling, and supplying an emulsion of the mixed oilproduced by the selected mixing ratio. Due to this, even if the requiredfriction coefficient changes in a certain range, it is possible toselect a mixed oil close to the required friction coefficient.Therefore, the effect is exhibited that it is possible to controllubrication finely with a high precision.

1-4. (canceled)
 5. A method of feeding lubrication oil for supplying anemulsion comprised of a lubrication oil and heated water mixed togetherto an inlet side of a rolling stand in cold rolling of a metal sheet,comprising storing two types of lubrication oils of differentcompositions and the lubrication oils and additives in separate tanks,setting in advance two mixing ratios of a first mixing ratio and secondmixing ratio in accordance with the friction coefficient for said twotypes of lubrication oil or a lubrication oil and additive, supplying afirst emulsion produced by said first mixing ratio to the inlet side ofthe rolling stand, increasing the emulsion supplying rate to reduce thefriction coefficient when the estimated friction coefficient duringrolling is larger than a target friction coefficient, switching to asecond emulsion produced by said second mixing ratio and supplying thesecond emulsion to the inlet side of the rolling stand when the increaseof said emulsion supplying rate reduces the friction coefficient, andswitching said second emulsion to said first emulsion to reduce theemulsion supplying rate and supplying the first emulsion to the inletside of the rolling stand when the estimated friction coefficient duringrolling is smaller than the target friction coefficient.
 6. A method ofsupplying lubrication oil in cold rolling as set forth in claim 5wherein at least one of said lubrication oils includes an additive.